I. Field of the Invention
This invention relates to a method and apparatus for controlling the temperature and pressure of confined substances. more specifically, a thermoelectric heat pump is utilized to maintain the interior of a pipe or vessel within a desired temperature and pressure range. As a result, undesired vaporization and solidification of substances stored within or moving through the vessel or pipe are prevented. The present invention may be utilized, for example, for keeping carbon dioxide within a vessel in liquid form.
II. Description of the Prior Art
The use of low pressure liquid carbon dioxide in fire extinguishing equipment is well known in the art. Its use is also known in the food processing, beverage and water treatment industries. Most known systems provide an insulated storage tank equipped with mechanical refrigeration apparatus in order to maintain the carbon dioxide at a suitable sub-atmospheric temperature. See, for example, U.S. Pat. Nos. 2,143,311; 2,068,119; and 2,287,873.
U.S Pat. No. 2,068,119 discloses a method of generating carbon dioxide gas from a supply of solid carbon dioxide. U.S. Pat. No. 2,207,662 suggests the use of a dwelling's hot water supply to prevent carbon dioxide in a tank from freezing upon the release of a portion thereof.
A major problem with these methods is that they require the use of the motors, fans, compressors, coils and the like which are associated with conventional mechanical refrigeration equipment. These components add undesirable weight and complexity to the system. One known method of avoiding this problem is disclosed in U.S. Pat. No. 2,525,570 in which a portable secondary tank having no refrigeration equipment is used for short term storage in conjunction with a stationary primary tank. The primary tank, however, must still be provided with the refrigeration equipment.
Another problem with conventional devices is that they commonly will not operate when the ambient temperature is below 0.degree. F. unless the tank is pressurized, by removing a portion of the carbon dioxide, heating the removed portion and returning it to the top of the tank.
Various forms of heat pumps are known in the art. See, U.S. Pat. Nos. 4,441,335; 4,441,901; 4,441,332; and 4,441,325. The use of small heat pumps for thermoelectric cooling is also known. The advantages of using heat pumps for the purpose of controlling the temperature and pressure of confined substances or for keeping carbon dioxide in liquid form, however, is not taught nor suggested in the art.
There remains, therefore, a need for an apparatus and method for storing carbon dioxide or other substances in liquid form or at a desired temperature and pressure which does not require the various components of a conventional refrigeration system. There further remains a need for a system which allows carbon dioxide or other substance within a tank to be heated by a source other than a hot water system provided for a dwelling.
It is an object of the present invention to provide an apparatus and method for controlling the temperature and pressure of confined substances which eliminates the need for the various motors, fans and compressors associated with conventional refrigeration systems.
It is another object of the invention to provide cooling means which causes vaporized carbon dioxide or other substance within a tank or pipe to condense to a liquid form.
It is yet another object to provide heating means to prevent liquid carbon dioxide or other substance within a tank or pipe from freezing when outside ambient temperatures drop, thus providing sufficeint vapor pressure for proper system operation.
It is yet another object to utilize a thermoelectric heat pump as both the cooling and heating means for the present invention.